A conventional imaging apparatus such as a digital camera has been provided with an imaging element containing a plurality of pixels for converting incident light into an electric signal. One of the products proposed in recent years is an imaging element having a plurality of types of photoelectric conversion characteristics.
One of the imaging elements having a plurality of types of photoelectric conversion characteristics is a linear/log transformation sensor that provides switching between the linear transformation for linearly transforming the incident light into electric signal based on the amount of incident light, and the logarithmic transformation for performing logarithmic transformation (Patent Document 1). According to this technique, the brightness range of the electric signal is wider than that of the imaging element that performs only the linear transformation. Thus, even when imaging an object having a wider brightness range, the brightness information can be represented by the electric signal.
The imaging element having a plurality of types of photoelectric conversion characteristics provides the output signal changed by a plurality of characteristics, and involves complicated computation in signal processing. To solve this problem, signal processing is made easy by characteristic conversion (or simply called “unification”) that uniformly converts the entire output signal using any one of a plurality of types of photoelectric conversion characteristics.
Incidentally, the aforementioned imaging element may have a variation in the input/output characteristics due to the difference in pixels. Thus, to remove such a variation, a method has been proposed to correct the output from each pixel and to find agreement with the reference output value (Patent Document 2)    Patent Document 1: Japanese Unexamined Patent Application Publication No. 11-298799    Patent Document 2: Japanese Unexamined Patent Application Publication No. 5-30350